In this column, Tim answers questions about
all aspects of electronics, including computer
hardware, software, circuits, electronic theory,
troubleshooting, and anything else of interest to
the hobbyist. Feel free to participate with your
questions, comments, or suggestions. Send all
questions and comments to: Q&A@nutsvolts.com.
■ WITH TIM BROWN Q & A
Post comments on this article at www.nutsvolts.
• Size of Satellite Dish
• Lump in Power Cable
Size of Satellite Dish
QBack in the ’70s and ’80s, satellite receiver dishes were anywhere from six feet to 18 feet in diameter, but now the dishes are only 18 to 24 inches in diameter. How is this possible?
— William Jenkins
Boca Raton, FL
AShort Answer: Improved technology. Long Answer: A satellite receiving "dish" is a parabolic antenna designed to focus the received weak signal at the focal point of the
parabola where a Low Noise Block (LNB) down converter
lowers the signal frequency to one more efficiently
handled by the receiver box electronics and amplifier to
boost the signal, while adding the minimum possible noise
to the signal for the range of channels used by the
transmitters on the satellite.
The transmitting satellite is located in a
geosynchronous orbit (stays roughly over the same point
on the Earth) approximately 22,300 miles ( 37,000 km)
directly (to the extent possible) above the Earth's equator.
The satellite has antennae which receive the signal from
an Earth-based station (like the head end facility of cable
TV), electronics to convert these signals, and antennae to
Re: Measuring Current With Clamp-On Ammeter:
Hi Tim! First of all, congrats on landing the Q&A
Empire. Always (was/now is again) my first stop when I
would peruse Nuts & Volts. For you, the sky is the limit in
not being tied to one topic per magazine. I really enjoyed
the first round in the October issue. There’s some
discussion I'd like to share and also an extremely useful
(and cheap) tool I use to quickly and safely measure AC
current. Quick background: I've worked engineering in
space/military/gov, 25 years with Hughes Aircraft and
currently own an engineering firm consulting with the big
The right-hand rule you showed in your article is great,
but confusing. Some mention of conventional current
would be helpful since depending on where you were
taught, the modern view of current flow is electron flow
(as the majority current carrier, except in PNP transistors)
where current flows negative to positive (hence, a left-hand rule). Just a thought, not a criticism.
As for my current measuring aid (see Photo 1), I
bought these very short extensions that are supposed to
allow you to plug in multiple wall warts in a power strip.
By separating the three wires, it gives you an awesome
place to clip your current clamp without any messing with
the equipment you're measuring. Also, you can make
certain there is no current going through the ground wire.
I've made tons of these for friends and colleges. Keep up
the great work and I look forward to your future articles.
Steven, thanks for the feedback. It is good to hear
from our experienced readers whose job is to keep me
straight. As far as not calling out conventional or electron-flow current, I did not think it was necessary to explain
why you need to clamp an amp probe on only one wire at
a time due to the effective cancellation of magnetic fields
between the two conductors. Plus, when you open the
conventional versus electron-flow "can of worms," you
polarize your readers who each think one or the other is
best (I think BOTH are best because each has its use in
explaining electrical charge flow), and there is the need to
take extra space to explain the two systems for those who
are new to electronics.
I like your idea for a "tool" to aid in measuring current
with an amp probe. I would just remind readers to
remember to use this device ONLY within its voltage and
current limits. Avoid exposed wiring or other conductors
which could be lethal when touched.
I have the easy job at N&V because all I have to do is
come up with answers. The authors of the other columns
have to come up with the questions (project ideas) and the
answers too. Our readers have the challenge to keep my
MAILBAG ■ PHOTO 1.
12 February 2015